"The time has come for the world to move in a new direction," Obama said in a speech that lasted more than 30 minutes and invoked his campaign rhetoric of hope and change. "We must embrace a new era of engagement based on mutual interests and mutual respect, and our work must begin now."

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Outlining the work the United States has done for its part, Obama admonished those who use anti-Americanism "as an excuse for our collective inaction."

"Make no mistake: this cannot be solely America's endeavor. Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone. We have sought, in word and deed, a new era of engagement with the world. Now is the time for all of us to take our share of responsibility for a global response to global challenges," Obama told attendees.

The president outlined what he called "four pillars" for the future: "non-proliferation and disarmament; the promotion of peace and security; the preservation of our planet; and a global economy that advances opportunity for all people."

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Afghanistan Tops U.S. List of International Challenges

As Obama tried to push attendees toward mutual cooperation, the administration is rethinking its strategy for Afghanistan and what to do next in the war that is growing increasingly unpopular.

"We will permit no safe-haven for al Qaeda to launch attacks from Afghanistan or any other nation," Obama said. "We will stand by our friends on the front lines, as we and many nations will do in pledging support for the Pakistani people tomorrow. And we will pursue positive engagement that builds bridges among faiths, and new partnerships for opportunity. But our efforts to promote peace cannot be limited to defeating violent extremists."

The president is exploring alternatives to a major troop increase, including a plan from Vice President Joe Biden to focus more on rooting out al Qaeda and the Taliban on the Pakistan-Afghanistan border, a strategy that could entail reducing troops.

"We're going to look very seriously at the circumstances on the ground, both political, security and economic, and how to best accomplish the goal of disrupting, dismantling and defeating al Qaeda," U.S. ambassador to the U.N., Susan Rice said on "Good Morning America" today. "The circumstances in Afghanistan are complex and evolving in the wake of the elections. It would be foolhardy for the United States and its partners not to take account of the circumstances as they evolve and adjust our goals accordingly."